This invention relates generally to cryogenic air separation and, more particularly, to the compression of fluids in the operation of the cryogenic air separation system.
In the operation of a typical cryogenic air separation system a number of compressors are employed. Some may be used to compress product, others to compress feed air, and others to operate internal circuits such as heat pump or liquefier circuits. Compressors are quite expensive to install, maintain and operate, and thus any improvement in the use of compression equipment in conjunction with a cryogenic air separation plant would be desirable.
Accordingly, it is an object of this invention to provide a cryogenic air separation system having an improved compression arrangement.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
Apparatus for producing at least one product by the cryogenic rectification of feed air comprising:
(A) a cryogenic air separation plant having at least one column;
(B) a base load air compressor and means for passing feed air to the base load air compressor;
(C) at least one booster compressor, and means for passing feed air from the base load air compressor to said booster compressor(s), and means for passing feed air from the booster compressor(s) to the cryogenic air separation plant;
(D) a multicomponent refrigerant fluid circuit comprising a multicomponent refrigerant fluid compressor and an expansion device, and means for passing refrigeration generated by the multicomponent refrigerant fluid circuit to the cryogenic air separation plant;
(E) a gear case, means for drivingly coupling the booster compressor(s) to the gear case, and means for drivingly coupling the multicomponent refrigerant fluid compressor to the gear case; and
(F) means for recovering at least one product from the cryogenic air separation plant.
Another aspect of the invention is:
A method for producing at least one product by the cryogenic rectification of feed air comprising:
(A) compressing feed air to a base load pressure to produce base load feed air and passing at least some base load feed air through one or more booster compressors;
(B) passing feed air from the booster compressor(s) into a cryogenic air separation plant having at least one column;
(C) compressing a multicomponent refrigerant fluid in a multicomponent refrigerant fluid compressor and expanding the compressed multicomponent refrigerant fluid to generate refrigeration;
(D) passing refrigeration generated by the expansion of the multicomponent refrigerant fluid into the cryogenic air separation plant;
(E) providing energy to operate the booster compressor(s) and the multicomponent refrigerant fluid compressor through a single gear case; and
(F) separating the feed air by cryogenic rectification within the cryogenic air separation plant to produce at least one product.
As used herein, the term xe2x80x9crefrigerationxe2x80x9d means the capability to reject heat from a subambient temperature system, such as a subambient temperature separation process, to the surrounding atmosphere.
As used herein, the term xe2x80x9ccryogenic air separation plantxe2x80x9d means a facility for fractionally distilling feed air by cryogenic rectification, comprising one or more columns and the piping, valving and heat exchange equipment attendant thereto.
As used herein, the term xe2x80x9cfeed airxe2x80x9d means a mixture comprising primarily oxygen, nitrogen and argon, such as ambient air.
As used herein, the term xe2x80x9cexpansionxe2x80x9d means to effect a reduction in pressure.
As used herein, the term xe2x80x9cproduct nitrogenxe2x80x9d means a fluid having a nitrogen concentration of at least 99 mole percent.
As used herein, the term xe2x80x9cproduct oxygenxe2x80x9d means a fluid having an oxygen concentration of at least 70 mole percent.
As used herein, the term xe2x80x9cproduct argonxe2x80x9d means a fluid having an argon concentration of at least 70 mole percent.
As used herein, the term xe2x80x9catmospheric gasxe2x80x9d means one of the following: nitrogen (N2), argon, (Ar), krypton (Kr), xenon (Xe) neon (Ne), carbon dioxide (CO2), oxygen (O2), helium (He) and nitrous oxide (N2O).
As used herein, the term xe2x80x9cvariable load refrigerantxe2x80x9d means a refrigerant mixture of two or more components in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the practice of this invention the temperature differences between the bubble point and the dew point for the variable load refrigerant is at least 10xc2x0 C., preferably at least 20xc2x0 C., most preferably at least 50xc2x0 C.
As used herein, the term xe2x80x9ccolumnxe2x80x9d means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as, for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. 
The term xe2x80x9cdouble columnxe2x80x9d, is used to mean a higher pressure column having its upper end in heat exchange relation with the lower end of a lower pressure column. A further discussion of double columns appears in Ruheman xe2x80x9cThe Separation of Gasesxe2x80x9d, Oxford University Press, 1949, Chapter VII, Commercial Air Separation.
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases is generally adiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).
As used herein, the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein, the terms xe2x80x9cturboexpansionxe2x80x9d and xe2x80x9cturboexpanderxe2x80x9d mean respectively method and apparatus for the flow of high pressure gas through an axial or radial turbine to reduce the pressure and the temperature of the gas thereby generating refrigeration.
As used herein, the term xe2x80x9ccompressorxe2x80x9d means a device for increasing the pressure of a gas.
As used herein, the term xe2x80x9cbooster compressorxe2x80x9d means a compressor which increases the pressure of feed air to a pressure greater than the base load pressure.
As used herein, the term xe2x80x9cproduct boilerxe2x80x9d means a heat exchanger wherein liquid from a cryogenic air separation plant, typically at increased pressure, is vaporized by indirect heat exchange with feed air. A product boiler may be a standalone unit or may be incorporated into the heat exchanger used to cool the feed air.
As used herein, the term xe2x80x9cturbine booster compressorxe2x80x9d means a compressor, typically a rotary impeller unit, used to increase the pressure of the gas, usually a fraction of the feed air, used to develop process refrigeration. The gas is turboexpanded to produce the refrigeration.
As used herein, the term xe2x80x9cproduct boiler booster compressorxe2x80x9d means a compressor, typically a rotary impeller unit, used to increase the pressure of the gas, usually a fraction of the feed air, used to vaporize liquid to provide gas product. The liquid is generally pressurized so that the vaporized gas is available at an increased pressure level.
As used herein, the term xe2x80x9cgear casexe2x80x9d means a device used to transmit shaft energy between energy providers, i.e. electric motors, steam turbines and gas expanders, and energy users, i.e. gas compressors, electric generators. The gear case is an integral combination of individual gears and gears with associated shafts, that allows the provision of the optimum shaft speed for each energy unit.